ARTICLE pubs.acs.org/est
Spectroscopic Evidence for Ternary Complex Formation between Arsenate and Ferric Iron Complexes of Humic Substances Christian Mikutta*,† and Ruben Kretzschmar† †
Institute of Biogeochemistry and Pollutant Dynamics, Department of Environmental Sciences, ETH Zurich, 8092 Zurich, Switzerland
bS Supporting Information ABSTRACT: Formation of ternary complexes between arsenic (As) oxyanions and ferric iron (Fe) complexes of humic substances (HS) is often hypothesized to represent a major mechanism for AsHS interactions under oxic conditions. However, direct evidence for this potentially important binding mechanism is still lacking. To investigate the molecular-scale interaction between arsenate, As(V), and HS in the presence of Fe(III), we reacted fulvic and humic acids with Fe(III) (1 wt %) and equilibrated the Fe(III)-HS complexes formed with As(V) at pH 7 (molar Fe/As ∼10). The local (
